Summary of Work: The interactions of anti-retroviral agents with drugs used to prevent opportunistic infections are increasingly appreciated. Most studies have evaluated two-way interactions despite the fact that most patients receive multiple drugs simultaneously. This study assesses the effect of multiple drugs additively and sequentially on the pharmacokinetics of stavudine, a hepatically metabolized drug. Stavudine has been shown to have no significant effects on the plasma levels of rifabutin, dauthromycin, or fluconazole. Conversely, those drugs have no influence on stavudine levels.